U.S. patent number 7,310,118 [Application Number 11/062,701] was granted by the patent office on 2007-12-18 for image display apparatus.
This patent grant is currently assigned to Victor Company of Japan, Limited. Invention is credited to Kazuhiro Kamimura.
United States Patent |
7,310,118 |
Kamimura |
December 18, 2007 |
Image display apparatus
Abstract
An image display apparatus has a hold-type display panel
composed of a matrix of pixels each holding an electric signal for
a predetermined period. In the image display apparatus, an
intermediate value detector provides an intermediate value signal
from adjacent two frames of a video signal having a first frame
frequency (60 Hz), a multiplier multiplies the intermediate value
signal by a coefficient that is smaller than 1, and an interpolator
inserts the coefficient-multiplied intermediate value signal into
the adjacent two frames of the video signal to provide a video
signal having a second frame frequency (120 Hz). According to the
video signal of the second frame frequency, an image is displayed
on the hold-type display panel.
Inventors: |
Kamimura; Kazuhiro (Tokyo-to,
JP) |
Assignee: |
Victor Company of Japan,
Limited (Yokohama, Kanagawa-ken, JP)
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Family
ID: |
34858241 |
Appl.
No.: |
11/062,701 |
Filed: |
February 23, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050184949 A1 |
Aug 25, 2005 |
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Foreign Application Priority Data
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Feb 25, 2004 [JP] |
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P2004-049227 |
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Current U.S.
Class: |
348/441;
348/459 |
Current CPC
Class: |
G09G
5/397 (20130101); G09G 3/3648 (20130101); G09G
2320/0257 (20130101); G09G 2320/0261 (20130101); G09G
2300/08 (20130101); G09G 2340/0435 (20130101) |
Current International
Class: |
H04N
7/01 (20060101) |
Field of
Search: |
;348/441,443,458,459,739,790,448-452,795 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Kurita, T. "Fundamental Deterioration of Picture Quality for Moving
Images Displayed on LCDs and Methods for Improvement", Technical
Report of IEICE EID2000-47 (Sep. 2000), pp. 13-18. cited by
other.
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Primary Examiner: Hsia; Sherrie
Attorney, Agent or Firm: The Nath Law Group Meyer; Jerald L.
Protigal; Stanley N.
Claims
What is claimed is:
1. An image display apparatus having an active-matrix display panel
composed of a matrix of pixels each holding an electric signal for
a predetermined period to display an image, comprising: a
frame-rate converter configured to convert a first video signal
having a first frame frequency into a second video signal having a
second frame frequency that is higher than the first frame
frequency; and a driver configured to display an image on the
active-matrix display panel according to the second video signal,
the frame-rate converter including: an interpolation frame
generator configured to generate an interpolation frame signal from
frames of the first video signal; a multiplier configured to
multiply the interpolation frame signal by a coefficient that is
larger than 0 and smaller than 1; and an interpolator configured to
interpolate the coefficient-multiplied interpolation frame signal
into the first video signal and provide the second video signal.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to hold-type image display
apparatuses such as liquid crystal displays and organic
electroluminescence displays, and particularly, to a hold-type
image display apparatus capable of presenting blur-reduced motion
images.
2. Description of Related Art
Image display apparatuses are classified into impulse-type display
apparatuses such as those employing cathode ray tubes (CRTs) that
momentarily emit strong beams to display images and hold-type
display apparatuses such as active-matrix display apparatuses that
employ pixels with a memory function to hold an image for every
frame period. An example of the active-matrix display apparatus is
a liquid crystal display (LCD) employing thin-film transistors
(TFTs). The LCD has pixels each including a TFT and a capacitor to
hold a written image signal for a given period.
The hold-type display apparatus has a draw back of causing a blur
when displaying motion images (hereinafter referred to as the
motion image blur). It has been understood that the motion image
blur is caused due to a slow response speed of liquid crystal. The
motion image blur, however, never solves by increasing the
liquid-crystal response speed because the blur is intrinsic to the
hold-type display. The blur problem and a solution for it are
described in Taiichiro Kurita, "Theory of Motion Image
Deterioration in LCD and Method of Solving the Same," IEICE
Technical Report, EID2000-47 (2000-09), pp. 13-18. The motion image
blur occurs not only on the LCD but also on the organic
electroluminescence display of active-matrix type. The method of
solving the motion image blur described in the above-mentioned
document shortens a hold time like the impulse-type display
apparatus.
The method described in the above-mentioned document needs a device
to shut a backlight in synchronization with a video signal. The
technique has a drawback of spoiling a feature of the hold-type
display apparatus of providing flicker-free images. The technique
has another problem of decreasing the brightness of a screen
because the technique shortens the emission time of each pixel.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of these
problems of the related art. An object of the present invention is
to provide an image display apparatus capable of fully using the
flicker-free feature of the hold-type display apparatus, preventing
a brightness decrease, and reducing the motion image blur.
In order to accomplish the object, an aspect of the present
invention provides an image display apparatus having an
active-matrix display panel (3) composed of a matrix of pixels each
holding an electric signal for a predetermined period to display an
image.
The image display apparatus includes a frame-rate converter (1) to
convert a first video signal having a first frame frequency into a
second video signal having a second frame frequency that is higher
than the first frame frequency and a driver (2) to display an image
on the active-matrix display panel according to the second video
signal.
The frame-rate converter has an interpolation frame generator (12)
to generate an interpolation frame signal from frames of the first
video signal, a multiplier (13) to multiply the interpolation frame
signal by a coefficient that is larger than 0 and smaller than 1,
and an interpolator (15) to interpolate the coefficient-multiplied
interpolation frame signal into the first video signal and provide
the second video signal.
The image display apparatus according to this aspect of the present
invention can fully utilize the flicker-free feature of the
hold-type display apparatus, prevent a brightness decrease, and
reduce the motion image blur. This apparatus needs no special
circuit such as a shutter to turn off a backlight, and therefore,
can be materialized at low cost.
The nature, principle and utility of the invention will become more
apparent from the following detailed description when read in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a block diagram showing an image display apparatus
according to an embodiment of the present invention;
FIG. 2 is a block diagram showing the details of a frame-rate
converter of the apparatus of FIG. 1;
FIGS. 3A to 3C explain operation of the frame-rate converter
according to the present invention and of the related art; and
FIGS. 4A to 4C explain effect of the present invention and of the
related art.
DETAILED DESCRIPTION OF EMBODIMENTS
An image display apparatus according to an embodiment of the
present invention will be explained with reference to the
drawings.
FIG. 1 is a block diagram showing the image display apparatus
according to an embodiment of the present invention.
In FIG. 1, the image display apparatus includes a frame-rate
converter 1 that receives an input video signal which is a
sequential scan signal having a frame frequency of 60 Hz. The
frame-rate converter 1 doubles the frame frequency of the input
video signal to 120 Hz. The image display apparatus according to
the embodiment is characterized by frame-rate conversion conducted
by the frame-rate converter 1. The details of this will be
explained later. The video signal of 120-Hz frame rate is supplied
to a driver 2. Based on this video signal, the driver 2 drives a
liquid crystal panel 3 to display an image at the frame rate of 120
Hz. The liquid crystal panel 3 is a hold-type display panel. The
display panel is not limited to a liquid crystal display panel. It
may be any active-matrix display panel composed of a matrix of
pixels each holding an electric signal for a predetermined period
to display an image.
FIG. 2 is a block diagram showing an example structure of the
frame-rate converter 1.
In FIG. 2, an image memory 11 receives the video signal of 60-Hz
frame rate. The image memory 11 has a capacity to store image data
of at least two frames. In this example, the image memory 11
consists of memory parts 11a and 11b each capable of storing one
frame of image data. Namely, a frame of image data is written into
each of the memory parts 11a and 11b at a write frequency of 60 Hz,
and the memory parts 11a and 11b are simultaneously read at a read
frequency of 120 Hz. The image data read out of the image memory 11
is supplied to an intermediate value detector 12 and an
interpolator 15.
The intermediate value detector 12 detects an intermediate value (a
central value in this example) between every corresponding pixel
values of the two frames. For example, a first pixel position of
the frame read out of the memory part 11a has a pixel value of 200,
and a second pixel position that corresponds to the first pixel
position and is read out of the memory part 11b has a pixel value
of 100. Then, an intermediate value between the pixel values of the
first and second pixel positions is 150.
The intermediate value detector 12 provides an intermediate value
signal representative of the detected intermediate values to a
multiplier 13. The multiplier 13 multiplies the intermediate value
signal by a coefficient of, for example, 1/2. The coefficient value
of 1/2 is only an example of a preferable coefficient value. It may
be any value greater than 0 and smaller than 1. The output of the
multiplier 13 is controlled by a limiter 14. The output of the
limiter 14 is supplied to the interpolator 15. The interpolator 15
inserts the data from the limiter 14 into the two frames of image
data from the image memory 11 and provides a video signal having
the frame frequency of 120 Hz.
FIG. 3A to 3C explain operation of the frame-rate converter 1 of
FIG. 2 and that of the related art and FIGS. 4A to 4C explain
effect of the present invention and that of the related art.
The operation and effect of the frame-rate converter 1 of FIG. 2
will be explained in detail with reference to FIGS. 3A to 3C and 4A
to 4C.
The video signal of 60-Hz frame frequency supplied to the image
memory 11 involves, for example, a step waveform shown in FIG. 3A
to display, among other pixels, pixels P.sub.200 each having a
pixel value of 200, pixels P.sub.100 each having a pixel value of
100, and pixels P.sub.0 each having a pixel value of 0. The step
waveform horizontally moves from the left to the right. At this
time, the motion image blur occurs with a width shown in FIG. 3A.
Pixel values at a pixel position X in FIG. 3A change as shown in a
graph of FIG. 4A in which an abscissa represents time and an
ordinate the pixel value. A hatched area in the graph of FIG. 4A
indicates visibility at the pixel position X depending on a
response of the pixel.
FIG. 3B shows the related art that shortens a hold time by shutting
a backlight. The backlight is shut for a half of 1/60 second, to
halve the hold time. The period during which the backlight is shut
is equal to a period in which a pixel value of 0 is applied to each
pixel. This technique makes the width of the motion image blur
narrower than that of FIG. 3A, to thereby reduce the motion image
blur.
Pixel values at the pixel position X in FIG. 3B change as shown in
a graph of FIG. 4B. This graph is closer to a graph to be plotted
by the impulse-type display apparatus. However, the graph involves
a large pixel value difference between adjacent frames, to cause
flickering. In addition, this technique decreases the brightness of
a screen as is apparent from a reduced hatched area shown in the
graph of FIG. 4B.
FIG. 3C shows a display state according to the embodiment of the
present invention. As explained above, the embodiment employs the
intermediate value detector 12 that provides an intermediate value
signal and the multiplier 13 that multiplies the intermediate value
signal by the coefficient of 1/2 and provides a video signal to be
inserted. In FIG. 3C, there is a section where the pixels P.sub.100
each having the pixel value of 100 change to the pixels P.sub.200
each having the pixel value of 200. To each pixel in this section,
a pixel value of 75 is applied as indicated with P.sub.75. In FIG.
3C, there is a section where the pixels P.sub.0 each having the
pixel value of 0 change to the pixels P.sub.100 each having the
pixel value of 100. To each pixel in this section, a pixel value of
25 is applied as indicated with P.sub.25. This technique makes the
width of the motion image blur narrower than that of FIG. 3A, to
thereby reduce the motion image blur.
Pixel values at the pixel position X in FIG. 3C change as shown in
a graph of FIG. 4C. This graph of the embodiment of the present
invention approximates a graph to be plotted by the impulse-type
display apparatus. In addition, the graph involves a small pixel
value difference between adjacent frames, to suppress flickering.
As is apparent from a hatched area in the graph of FIG. 4C, the
embodiment can suppress a screen brightness decrease.
According to the embodiment explained above, the intermediate value
detector 12 in the frame-rate converter 1 provides an intermediate
value signal, which is used to generate an interpolation frame
signal. This technique of generating an interpolation frame signal,
however, does not limit the present invention. The present
invention may employ, for example, a motion vector detector
employing a matching method to generate an interpolation frame
signal. Also, the present invention is not limited to generating an
interpolation frame signal according to adjacent two frames. For
example, the present invention can generate an interpolation frame
signal from any number of frames such as four frames. Instead of
directly inserting an interpolation frame signal, the present
invention multiplies the interpolation frame signal by a
predetermined coefficient to reduce the level of each pixel value
and then inserts the coefficient-multiplied interpolation frame
signal into a video signal to display. This is an important
characteristic of the present invention. Without departing from the
spirit of the present invention, many amendments or modifications
will be possible.
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